A vast number of commercial products that are difficult to produce synthetically may be produced by fermentation. Such products including alcohols (e.g., ethanol, methanol, butanol, 1,3-propanediol); organic acids (e.g., citric acid, acetic acid, itaconic acid, lactic acid, gluconic acid, gluconate, lactic acid, succinic acid, 2,5-diketo-D-gluconic acid); ketones (e.g., acetone); amino acids (e.g., glutamic acid); gases (e.g., H2 and CO2), and more complex compounds, including, for example, antibiotics (e.g., penicillin and tetracycline); enzymes; vitamins (e.g., riboflavin, B12, beta-carotene); hormones; and also products commonly used in the consumable alcohol (e.g., beer and wine), dairy (e.g., in the production of yogurt and cheese), leather, and tobacco industries.
Ethanol has widespread application, including, as an industrial chemical, gasoline additive or straight liquid fuel. As a fuel or fuel additive, ethanol dramatically reduces air emissions while improving engine performance. As a renewable fuel, ethanol reduces national dependence on finite and largely foreign fossil fuel sources, while decreasing the net accumulation of carbon dioxide in the atmosphere.
Typically ethanol is produced by liquefying starch-containing material followed by sequential or simultaneous saccharification and fermentation. Liquefaction involves gelatinization of starch simultaneously with or followed by addition of alpha-amylase in order to degrade starch into dextrins. When producing ethanol the liquefied starch-containing material is saccharified. Saccharification is a step in which dextrins are converted to low molecular DP1-3 sugars that, e.g., can be converted by a yeast into ethanol.
U.S. Pat. No. 5,231,017A discloses an ethanol production process comprising (a) liquefying raw material in the presence of an alpha-amylase, (b) saccharifying the liquefied mash in the presence of a glucoamylase, (c) fermenting and (d) recovery of the ethanol, wherein a protease is introduced to the liquefied mash during saccharification and/or fermentation.
Canadian Patent 1,143,677 disclose a process of producing ethanol from amylaceous raw stock by hydrolyzing said raw stock material with an amylolytic enzyme and a cellulase preparation derived from a culture of Trichoderma königii comprising a complex of hydrolytic enzymes including C1-enzyme, exoglucanase, endoglucanase, cellobiase, xylanase, beta-glucosidase, protease and a number of amylolytic enzymes.
Mullins et al., “Biomass” 16 (1988) 2, pp. 77-87, demonstrated that addition of alkaline protease to mash results in an increase in amino nitrogen sufficient to support accelerated rates of ethanol fermentation.
There is a need for further improvement of fermentation product production processes.